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Re: [libvirt] [PATCH] fwrite: silence __wur without using inline



On 01/03/2013 11:16 AM, Paul Eggert wrote:
> Thanks for fixing that.  I'm still puzzled about
> why the problem happened with libvirt.

Why libvirt, and not detected elsewhere?  Probably because libvirt does
this at configure time:

    AH_VERBATIM([FORTIFY_SOURCE],
    [/* Enable compile-time and run-time bounds-checking, and some warnings,
        without upsetting newer glibc. */
     #if !defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__
     # define _FORTIFY_SOURCE 2
     #endif

and the inline in question is only turned on when _FORTIFY_SOURCE is
enabled.  Packages where no one uses _FORTIFY_SOURCE by default would
never hit the issue.

> It's better now that
> stdio doesn't depend on extern-inline, but I worry that whatever
> bug the libvirt folks were having with stdio and extern inline
> might crop up when extern inline is used in other include files.

The elided code was not using _GL_EXTERN_INLINE, but _GL_INLINE.  They
have different semantics, but I'm hard-pressed to say _which_ semantics
are right from just those names.  If I understand correctly, we _want_
the semantics where the inline function is _always_ inlined and never
emitted as a linkable entry point, but I'd have to refer back to C99 and
the gcc manual to see which use of inline and possible __attribute__
combinations guarantees that point.  I've seen code that uses the name
ELIDABLE_INLINE for the specific combination we want used in header
files; maybe it's worth adding a name _GL_ELIDABLE_INLINE into
m4/extern-inline.m4 to make it easier to use the results.

> 
> One minor improvement is that we can limit the workaround to
> glibc versions that have the problem, so I pushed this further
> change.

Thanks for that improvement.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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